This invention relates to twin tube shock absorbers having gas seal means therein and, more particularly, to such devices utilizing integral main seal and gas seal portions. The shock absorber of the present invention is particularly useful in MacPherson strut vehicle suspension systems.
Shock absorbers for use in a vehicle suspension system of the type including a double-walled cylindrical structure which includes an inner oil cylinder and an outer reservoir chamber are known and have been widely used in the art. In this type of shock absorber any air that is trapped in the working or oil cylinder as a result of operation of the shock absorber is bled into the reservoir chamber. During the downstroke of the piston in the oil cylinder the air in the reservoir chamber must be prevented from entering the oil cylinder. In the prior art, various one-way valves have been provided in a narrow passage which communicates between the working cylinder and the outer cylinder. These valves have disadvantages in that they are complicated mechanical devices, typically comprising a spring-loaded ball valve and valve seat, and are not easily mounted in the narrow passage that connects the working and reservoir chambers. Other gas seal techniques have been provided which eliminate the complicated mechanical solutions of the prior art and are illustrated in U.S. Pat. No. 4,108,287. These prior art devices utilize a multiple seal configuration wherein a first seal is provided between the piston rod and the cylinder cap to trap the oil within the shock absorber. A second flexible seal is spring loaded in the passage way and functions to prevent the passage of gas into the inner or working cylinder. These prior art devices have the disadvantage that they are difficult to assemble and more expensive to manufacture.
These and other disadvantages are overcome by the present invention wherein there is provided a gas seal for a double-cylinder or twin tube shock absorber which is of an integral, one-piece construction which readily can be mounted in the passageway connected to the working cylinder with the reservoir chamber and which simultaneously provides the piston rod and gas sealing functions.